The present invention relates to a semiconductor light emitting element and a manufacturing method thereof, and more specifically, to a semiconductor light emitting element which is suitable for a semiconductor light emitting apparatus with a high light emitting efficiency.
A storage apparatus utilizing an optical recording has a large storage capacity and is characterized by a long life and a high reliability due to non-contact, so that this type of apparatus is broadly utilized. As the light for use herein has a shorter wavelength, a recording density can be raised, and hence, blue to green light emitting elements are to be used. Moreover, some novel light emitting elements have been realized such as white LED""s which obtain a white light by combining a blue LED with a YAG fluorescent substance.
As the blue to green light emitting elements, a light emitting diode (LED) and a laser diode (LD) having a high luminance have been now obtained with a GaN-based material.
As a crystal growth technique of this GaN-based light emitting element, much attention has been paid to epitaxially laterally overgrown (ELO) in recent years.
FIG. 11A is a sectional view showing an outline of a growth state in ELO. First, a selective growth mask 2 is formed on a sapphire substrate 1 (FIG. 11A), and the growth of a GaN-based film is then performed with ELO, so that for a crystal defect, the GaN-based film grows so as to embed the selective growth mask owing to a difference of a growth speed in ELO between lateral and vertical directions (FIGS. 11B and 11D). Moreover, in this case, since the crystal defect is generated along with the fast lateral direction growth, there is very little transition in the GaN film by ELO on the selective growth mask. When an epitaxial layer is stacked onto this film to obtain an element structure (FIG. 11D), a defect density of a substrate is very low, and therefore a semiconductor light emitting element having excellent light emitting properties can be obtained.
In a light emitting center (D/A) type blue LED structure of the light emitting diodes (LED) with the high luminance in which such a GaN-based material is used, InGaN which is an active layer is doped with Si as a donor and Zn, Mg or the like as an acceptor, a desired light emitting wavelength is to be obtained in a light emitting center, not in a band end, and therefore in addition to a visible light, numerous ultraviolet (UV) lights are generated. That is to say, in the case of In 13% in the composition of this active layer, the light emitting wavelength in the band end of a center wavelength 400 nm is about 365 nm, but besides the ultraviolet light from the light emitting center, the ultraviolet light from this band end is also present, and as injection current is increased, a proportion of the light emitted from the band end increases. However, this ultraviolet light is not effectively utilized, so that a light extraction efficiency remains at a low level.
Moreover, in a UV light emitting LED which decreases In composition and generates only the ultraviolet light from the active layer, the generated ultraviolet light is not effectively extracted, and an external quantum efficiency remains to be low. Furthermore, the aforementioned ELO technique is utilized only for transition reduction.
Additionally, in order to enhance the light emitting efficiency, in the GaN-based semiconductor light emitting element, it has been proposed to contain the fluorescent substance at least one of p-type and n-type semiconductor layers (Japanese Patent Application Laid-Open No. 82849/2000).
However, it is difficult in manufacture to contain a particulate fluorescent substance in the semiconductor layer generally formed by vapor phase growth.
The present invention has been developed to solve the problem, and an object thereof is to provide a semiconductor light emitting apparatus high in light extraction efficiency.
According to the present invention, there is provided a semiconductor light emitting element comprising, as a lamination structure:
an insulating substrate;
GaN-based stacked films stacked/formed on said insulating substrate, one of these films being a GaN-based film grown by using a selective growth mask material layer containing a fluorescent substance for converting an ultraviolet light to a visible light; and
an active layer, formed on the GaN-based stacked films, for emitting at least an ultraviolet light component.
According to the semiconductor light emitting element, since a fluorescent substance is mixed beforehand into a selective growth mask layer for ELO, it is possible to convert an ultraviolet light which has heretofore failed to be effectively utilized to a visible light in the vicinity of an active layer, and a bonding efficiency with the fluorescent substance can remarkably be enhanced.
A topmost layer may further preferably be provided with a protective layer containing the fluorescent substance, and a light emitting efficiency can further be enhanced by raising a conversion efficiency to the visible light from the ultraviolet light.
A lens may be formed on an insulating substrate back surface side, thereby it is possible to extract the light from the back-surface side, and the present invention can also be applied to flip chip mounting or the like.
A thickness of the selective growth mask layer containing the fluorescent substance may be 50 nm or more, 20 xcexcm or less.